If you plan on cycling the new Trans-Labrador highway, it's probably about as epic as the Dalton in Alaska or the Dempster in the Northwest Territories. The final phase of this unpaved highway just officially opened this month so if you are a brave soul you could be one of the first cyclists to traverse this wilderness. There won't be any services for hundreds of kilometers at a time, and the blackflies in the muskeg will most likely drive you insane!
The other option for a loop if you do go up to Labrador is to take the Relais Nordik between Blanc Sablon and Natashquan. I've been dreaming of going on this boat trip. I imagine you could do quick bike rides while the ship loads/unloads at the small coastal communities along the way.