Route Verte from Maine, USA to Quebec City - then Montreal

Hi,
We are planning a trip on our road tandem for about 3 weeks in August. We will be following the Route Verte and would like any helpful info for the trip. I especially need to know if we cross the border from Maine, is there anywhere close to leave our car during our bike ride? Also, has anyone done this part of the Route Verte, and do you have recommendations or info on road conditions, campsites or WARM SHOWER hosts? Are there any parks (similar to US state or National parks) along the way? Some one recently told us it is difficult to get into/out of Montreal by bike... is this true?
Thank you so much and if you need a warm shower in Maine, check us out!