Looking at the aerial maps it looks as though there may be a trail down to Gowan lake from the 471 forest road (NW of the lake). Is that the case and how accessible is this likely to be in the winter?

I've bushwhacked to Gowan from the Norway Road before. That was a long, rugged bushwhack. It looks to me, from studying google maps, that the trail you are referring to is a logging road (it didn't exist when I did my bushwhack). It looks like it goes to the edge of the BWCA boundary, so it stops about 1/2 mile from the lake. Of course it's possible that there is a trail to the lake that doesn't show up on sat photos....

The only way those roads would be plowed would be if someone was logging back there currently. Not real likely, but you never know. Also there used to be a gate on the Norway road.

There used to be a portage from the Norway road to the north arm of Trout Lake. Not sure if that's still maintained or not, but it was a nice way to get into that area. There used to be a fire tower there, and I believe the portage accessed that fire tower.

Hope this helps. Perhaps someone with more current knowledge will be along.