You don't really need a set of grad ND filters, just one 3-stop or 4-stop, unless you are taking a huge variety of images that need them. A decent one will cost around $100 each [I use Singh Ray]. Also, you speak of having them fit your lenses, but the filters are rectangular and they sell holders and adapters for different lens diameters. If you are not going to be switching from using a filter to not using one, a holder is OK. But with light changing as quickly as it does, it is much easier to hand-hold the filter. Just have to make sure you cover the entire lens, which just takes a couple of times not covering to make you pay attention. After that it begins to feel more natural/comfortable.

There are variable ND filters that screw onto a lens, but they are not graduated and there are problems with getting an"X" shaped aberration in the image. If you simply want a filter to reduce light in the whole picture, then you can buy the solid ND filters [which ARE sized to screw into a lens], but I find that having a circular polarizer is much more useful. The camera settings can compensate very well for too much light without an ND filter. And if you do not already, you should try bracketing at least 3 shots, sometimes more - on a tripod - then you can choose the best exposure to work on or combine them in HDR.

The area in Canada you are visiting is beautiful. You should find lots of photographic opportunities! Have fun...
Susan