Both the G7XIII and SX740HS are 20MP cameras. Both use SD memory cards, both use the same NB-13L battery that's good for around 200 to 300 shots (your "mileage"
will vary) and both have 3" LCD monitors. Neither camera has a hot shoe for use with an accessory flash. Both cameras use Canon's latest "Digic 8" processor (rumors are that Digic 9 are coming in some future models).
But that's about where the similarities end. They're designed and intended for somewhat different purposes, and are priced differently.
The SX740 HS sells for about $400, while the G7X Mark III costs about $750.
Because of the variation in sensor sizes used in compact digitals such as these, it's common practice to refer to them using "35mm equivalent" focal lengths, rather than actual focal length range, in order to be able to compare different models.
The SX740 HS is primarily a "super zoom" compact digital camera. It uses a 40X zoom that makes for "35 equivalent" range from 24mm to 960mm. The camera uses a tiny 1/2.3" CMOS sensor to achieve this. The dimensions of the sensor are approx. 6.25x4.75mm, or around 29 sq mm (into which are crowded 20 million pixels... or nearly 700,000 pixels per sq mm). This results in a 5.5X to 5.6X lens "multiplier" (as compared to 35mm "full frame").
Further, the SX740 HS lens' variable max aperture is somewhat limited to f/3.3 (at wide angle) to f/6.3 (at the telephoto end). Along with that smaller sensor, this limits the camera's usability in low light conditions and the enlargeability of its images. Canon limits the camera's ISO (sensitivity) range to 3200 maximum, but that will likely be unacceptably "noisy". I would be surprised if higher than ISO 400 or 800 is actually usable for a lot of purposes.
The G7X Mark III is a more advanced, premium model using a larger sensor that makes for a much more modest zoom range: "35mm equivalent" range from 24mm to 100mm. The camera uses a 1" CMOS sensor (also called "CX" size), measuring approx. 13 x 9mm for a total of 116 sq mm, into which 20 million pixels are fitted. That makes for approx. 172,000 pixel sites per sq mm. It also makes for a 2.7X lens multiplier (as compared to 35mm/full frame), which limits the extremes to which the zoom lens can go.
However, this larger and far less "crowded" sensor should allow much higher ISO to be used, to be able to keep shooting in lower light conditions. Canon sets a much higher maximum of ISO 12800, though users may want to limit it somewhat lower. The lens itself is "faster" too, with max aperture from f/1.8 (wide) to f/2.8 (tele), which will further allow for lower light shooting, as well as make for moderately shallow Depth of Field effects.
In a nutshell...
The SX740 HS would be a useful camera to photograph wildlife at a distance, so long as the light is good.
The G7XIII, on the other hand, would be a better portrait camera and more usable indoors or in other lower light conditions. The GX7III's images also should be more "enlargeable", likely making it more useful for scenic landscape or architectural shots.
The SX740HS is "JPEG only". The G7XIII can take JPEGs too, but it also is able to capture RAW files (which allow quite a bit more user adjustability after the fact, in post-processing... although the larger files will use more memory card space).
Both cameras can shoot video up to 4K resolution.
Some comparisons:
https://www.bhphotovideo.com/c/compare/Canon_SX740_HS_vs_Canon_G7_X_Mark_III/BHitems/1427176-REG_1498748-REGhttps://cameradecision.com/compare/Canon-PowerShot-G7-X-Mark-III-vs-Canon-PowerShot-SX740-HShttps://www.imaging-resource.com/cameras/canon/sx740-hs/vs/canon/g7x-mark-iii/https://www.apotelyt.com/compare-camera/canon-g7-x-mark-iii-vs-canon-sx740More detailed reviews of each model:
https://www.dpreview.com/products/canon/compacts/canon_g7xiiihttps://www.dpreview.com/products/canon/compacts/canon_sx740hsEDIT: Someone above suggested yet another model... the Canon G3X. This is sort of a premium quality compromise between the G7XIII and SX740HS.
The G3X doesn't have quite as much telephoto "reach" as the SX740HS.... But it's 25X zoom is a whole lot more powerful than the G7XIII's. And it uses a larger sensor for better image quality and low light capability. In the end, the G3X would be a more versatile camera.... capable of doing much of what either of the other two models offer.
Of course, it also costs more.... $850 for the camera alone. It also doesn't have a built-in viewfinder, like the other two cameras. An accessory viewfinder is available and recommended, but brings the total cost to $1150.
The G3X has a hot shoe, too... which that auxiliary viewfinder uses when it's installed. But it also means this camera can be used with an accessory flash, which can be very handy at times. The built in flashes in all these cameras are pretty small and not very powerful. Even a smaller accessory flash like the Canon 270EX is considerably more powerful and capable than the built-in... plus has it's own power supply so it doesn't rapidly drain the camera's rechargeable battery. The G7XIII and SX740HS don't have hot shoes, so they cannot be used with a flash like this.
I don't know why the G3X is bundled with the $300 EVF-DC1 viewfinder. It also appears to be able to use the EVF-DC2, which is $100 less expensive. There may be differences in capabilities of these viewfinders, which should be considered before committing to one or the other. I really don't know.
https://www.bhphotovideo.com/c/product/1187753-REG/canon_powershot_g3_x_digital.htmlhttps://www.bhphotovideo.com/c/product/999967-REG/canon_speedlite_270ex_ii_essential.htmlhttps://www.bhphotovideo.com/c/product/1318788-REG/canon_1727c001_evf_dc2_electronic_viewfinder_black.htmlOne thing is certain, you can always rely upon UHH to help you spend your money!