Horne Lake is actually quite deep and it stays pretty cool even in the summer. May would be a great month so you may want to fish to where the Qualicum River flows into the lake near the campground. Most of my fishing was done on Spider Lake, but I have seen trout cruising the drop off along the lake shore and there are some old submerged stumps too. You'll find some very nice smallmouth at Spider and some decent rainbows too. Its not too far away from Horne, but it gives you another option as well.
As for gear, a medium light spinning rod would work and the old gang troll and worm ususally is a good stand by. Definitely a 10ft salmon rod would be too big but you can get relatively inexpensive but decent quality gear at most tackle shops.
Good cutthroat bait (for gang trolling) is hot dog - small pieces. The fish like it and you can even eat 'em too if you get hungry
Good luck,
GHC