Ive used both LowePro and Think Tank. Love them both. the LowePro site has a bag finder option where you enter your gear and it finds the bag that might fit it all. Think Tank may have one too. I'm currently using a ThinkTank Street Pro.
I too was a Nikon person. After lugging around all my gear through 9 national parks, I found I wasn't using what I brought because of the weight. I remembered a Nat Geo photographer talking about how he started using the OMD for his shoots. I traded in all my Nikon gear for the OMD Mark 5II. I am thrilled with my decision!!! The Mark 5 has a weatherproof body, dust sealed, 5 axis image stabilization and a host of other features. I paired it with a 14-150 II zoom, which is also dust, water, sealed. I've used it now for more than a year and love the quality of images, it's portability, everything. The fun is back. I've added a super zoom and a couple of fast primes since. The camera has a setting to produce a 60mp image and it will do a live composite image (it's the only camera that will do this). My whole kit weighs less than my beloved Nikon and just the 70-200 f4.
If you do go this route, be sure to get Mastering the Olympus OMD Mark 5 II and really read it. The capabilities of this camera are vast! I'm still discovering new functions.
For what it's worth, the 16mp Olympus OMD Mark 5II has a setting that will produce a 40 mp image and the new Oly m1 II will do 60mp.
I went into a local camera store near where I worked. I was looking for a camera to use with my very fast.movong grandchildren and was frustrated with a shutter lag that captured nothing! They recommended a Nikon n60 because of the metal mount. Up til last year, I was a loyal Nikon girl and captured thousands of happy memories.
But the weight got to me. I wasn't using that wonderful glass. So I traded in all my gear for an Olympus OMD Mark 5 II. The joy is back!
I've used both Borrow Lenses and Lens Pro 2 Go with great success. Borrow Lenses may have more inventory in micro 4/3s.
Niagara is a must! Bring a "raincoat" for your gear as Cave of Winds and Maid of the Mist are musts! Finger lakes are charming, big wine country too. Vermont is gorgeous. If you're thinking of going around Columbus Day, reservations would be a very good idea as it's peak foliage season.
Try renting a few. How do you feel about weight of your equipment? Try a micro 4/3s also. Strongly suggest trying the Olympus OMD m1 ll or the m5 ll. I was a Nikon woman for years until a 6 week National Parks tour. I loved my D7000 and my lenses,but by the end of the trip, when I needed an assist to get my camera bag into the overhead, I was done. I turned in all my Nikon gear for the Olympus m5 ll. I couldn't be happier and more liberated. I've had it and the 14-150mm ll (28 - 300 full frame equivalent) at the start and have added a couple of fast primes plus a super zoom. The whole kit weighs less than my Nikon and my 70-200 f4 lens. Try before you buy! Borrow Lenses and Lens Pro to Go are both great companies to rent from.
I've used both LensPro to Go and Borrow Lenses. Great experience with both. They deliver to you and the return is simply a matter of dropping off at FedEx. Lenses come week packed.
Look for a photo specific tour. I took one (wish I could remember which one, but too many years have passed) and the boat was designed with tiers so everyone could have a good shot. I used a monopod. It was coupled with a short land hike.
Take the one lens that will give you the broadest focal length range. Last summer my husband and I completed a nine national park tour. I brought my Nikon D7000 and my 70-200, a rented wide angle zoom, my nifty 50, and 16-85. Pain in the neck, back, etc. The weight was a real deterrent. I wound up using the 16-85 most of the time. The others were just dead weight. I was ok with having to use a higher ISO. The bigger, heavier lenses were dead weight. If you do go with your favorite, get a BosStrap camera strap, it will really save your neck and increase your enjoyment.
P.S. When I got back home I traded in all my beloved gear for am Olympus OMD Mark 5 II and a 14-150mmII lens. I couldn't be happier. I have added other lenses since but my gear bag still weighs only a fraction of what it did. Have a great trip.