The current standard for mapping a canoe/kayak/paddlecraft launch is a single point at the water's edge, preferably at the end of a trail leading to it, tagged with:
    canoe=put_in;egress
Add any further descriptive tags.

For more information see:
* Michigan notes about tagging water features: https://wiki.openstreetmap.org/wiki/Michigan#Water
* Michigan water trail mapping project: https://wiki.openstreetmap.org/wiki/Michigan/Trails#Water_Trails
* Paddlecraft rendering: https://openstreetbrowser.org/#map=14/42.7385/-84.5501&basemap=osm-mapnik&categories=paddling_hazards,paddling_routes,paddling_amenities