Now that is a good question. And truthfully I do not know the answer.. It has been a long time since I read the signs on that bridge..
If the sign says "Trucks use only the ___ 2 lanes" you can use them
If the sign sys Trucks only in the ___2 lanes" you can not. (This assumes 2 lanes)
But ask, that's the best way, Ask,
Also the tunnel is not that far away, Directions if you need 'em (Shortest route, right hand turn off of Jeffereson mkes it easier)
N on I-75 first exit shoudl be M-10, south on M-10 till road dumps you on Jefferson headed west toward tunnel entrance right turn to tunnel. Check to make sure you can take a motor home through tunnel (propane restriction may or may not prohibit) I do not recall ever towing my trailers through tunnel and now with the Patriot garbage I won't be travelign to Canada any time soon.
Home is where I park it!