After I think about this, you are probably better off starting in Niles, coming up M140 to Watervliet, getting on Van Buren Trail to South Haven, then east on KalHaven to KRVT to Kalamazoo, then turning north up Douglas Ave. That goes all the way to Grand Rapids, where it become Division Ave. Make your way through the north end of downtown out to 5/3 Ballpark (Comstock Park.. I think there is a bike route through the NW corner of the city that will cross the river), and you can get on the White Pine there.