You don’t have to plan from scratch. These rides run through Slocan or pass close by, mapped and written up by route publishers around BC. The full maps and turn-by-turns live on their sites.
Loop Kaslo Slocan— Trails BC · 221 km route, 2 km of it through Slocan
Selkirk Splendor (BC Only)— Adventure Cycling Association · 355 km route, just clipping the edge of Slocan
Getting there with a bike: province-wide buses, ferries, and shuttles are listed under Transport (some serving Slocan may be listed there rather than here).