There's a great day use area in kluane at Kathleen lake, just shy of two hours from Whitehorse. We took my girlfriends parents there and they loved it.

You can have a nice picnic in the big warming/cooking hut, which is super accessible if your dad is having trouble with mobility.

The building is totally closed in with big windows and lots of tables. It's rarely busy and there's a nice wood stove in there for warmth and ambiance, with firewood available outside. Bring an axe.

The lake is gorgeous and There's a nice boardwalk around the bay for an after dinner stroll.

Anothwr nice spot is the town of Carcross. There's a neat little shopping plaza that's all done on a boardwalk with tiny houses lining it that sell crafts and amazing coffee. There's an awesome new interpretive centre called skookum Kim house, with carcross tagish First Nation staff on site who happily share their culture and history.

Good grayling fishing from the bridge in town, over a channel connecting two big bodies of water where the fish move between a pinch point.

Lots of road accessible lakes closer to Whitehorse, including some stocked with rainbow trout. Message me and I'll share some hidden gems. Heck I'll take you fishing on if you twist my arm.

Enjoy the yukon. It's a magic place and that's wonderful what you're doing for your dad.