G'morning from Casa Grande, AZ. BOY!!....that trip you're planning sound WONDERFUL!!
Wife and I have been full timing (originally out of Duluth, Minnesota) since 2005. We're currently official residents of S. Dakota where she grew up in the Mitchell, SD area and have relatives we've visited in the Sandpoint, ID area. Have also been out to the Maritimes a few times, but, like you, have yet to hop over to Newfoundland. Are you planning to spend time in Newfoundland??
There are so many places along your route to see that it's pretty difficult beginning to make suggestions as to what NOT to miss.
Ofcourse, the Sandpoint area is beautiful to begin with. Then as ya head East through Montana, we'd sure suggest staying on Interstate 90 through Montana on into the Black Hills area of S. Dakota (maybe dropping down for a visit to Yellowstone/Tetons first). Think about a stop near Gillette, WY to see Devils Tower, but then a little further East take a short run to stay in Deadwood, SD (just S. of I-90) between Spearfish and Rapid City. Spend a few days touring the Black Hills. Park your rig and use your tow vehicle or car (if your towing) and see Mt. Rushmore, drive the Needles Hyw., and drive the wildlife loop in Custer Park.
Once ya leave the Black Hills and head East again, we'd suggest following I-90 through S.D., Minnesota and on into Wisconsin, THEN unless ya need to, avoid Chicago and make your way NE from around LaCrosse, WI up toward Greenbay and on NE over the top of Lake Michigan to Mackinaw City, MI area and stay a day or tow at St. Ignace. While there, leave your rig in St. Ignace and take the short passenger ferry out to Mackinac Island for the day.
Now...once in St. Ignace, you've got to decide whether ya REALLY, want to swing S. through lower Michigan then East into Ohio, Pennsylvania, New York, etc....OR....(and this is what we'd suggest), depart St. Ignace N. to Sault Ste. Marie and on into Ontario, heading East toward Ottawa/Montreal, then cross back into the States going into Vermont, New Hampshire and into Maine before heading back into New Brunswick and East into Nova Scotia. The reason we'd suggest this is that the run from back in LaCrosse, Wisconsin, through Chicago, to Ohio, Penn., and lower New York, isn't all that scenic.
Once your in Nova Scotia, you'll need to take a ferry out to Newfoundland if you're headed there. Now we haven't yet done this so others will need to help ya there, BUT, wherever ya head, DO NOT MISS a few days visit to Quebec City, when heading West on your way back home through Canada. Old Towne Quebec is a WONDERFUL place to spend time and DO spend both day time and evening time in Old Towne Quebec City.
Awww.....this is gettin too long!
As mentioned, there are SO MANY things and places to see along your route, it's tough to relate them all here in this post. Once ya decide on a route, maybe ya can ask specific questions about points along the way. We'll try to help, and I'm sure others will provide additional info.
Have a GREAT TRIP!...YOU'LL LIKE IT!!
Steve & Lynette