Only two roads to drive, the Ingraham Trail and one south to Edmonton. The trail provides some access spots for lakes along it, but you would need some floating transportation to fish them. I only use a canoe, so it's possible to get fish and not have a motor boat. Plus, one portage and all the motor boats are behind you. The road to Edmonton mostly leaves good fishing territory, until you hit some larger rivers 3-8 hrs south of YK.
Grayling? Only in spring and early summer on the road south a few hours drive. There is a small run of fish in a creek about 5 mins out of town but fishing is closed on it. And that happens in late April, early May. Some guys have grayling luck in early summer from motor boats around the island of Great Slave, not too far from YK, but by August, the water is too warm.
I have people come visit and want to catch fish in August. It's tough. This entire Territory is set up for winter. Temps to -40 and 4-5 ft of ice. When the water gets "warm" in August, our peak water temp time, lots of things shut down. As Drifter said, there are still large lakes that keep their cold water through August, and that is where the best fishing will be. If you come up for a good time and to see some good country, and fish is just gravy, you will have a great time.
I've even caught pike in 50-60 ft of water trolling heavy weight and a spoon for lake trout in August.
