James
Spent 12 years up north - NWT and Yukon - and loved catching Grayling. Depending on how big you expect a 4 or 5 weight is sufficient. They aren't picky about flies but my preferred method is dry because they will often jump out of the water and take the fly on the way down - a blast to watch. BWOs, foam beetles, ants, black gnats and mosquito patterns worked best for me - as for wets, I found something with some sparkle in it worked best, bead head hares ears, bead head PTN or Prince nymph. One of the most most successful patterns in the Yukon was a black wooly worm with red wire rib, red tail and gold bead head. Caught a lot on yellow or golden stonefly patterns too.