Great news that you already have the b2 visa, now you can plan.
First thing is you must be aware that you technically cannot spend 6 months in the US then cross into Canada and hope to cross back to the US if you decide to do so. You should be able to spend 3 months in the US, go into Canada for 6 Months then cross back to the US for another 3 months but...
You can spend 6 months in Canada then cross into the US and spend 6 months there but...
Now the buts, in the first instance the general rule is that once you are landed in the US and are hopefully granted 6 months, the clock starts ticking. Going in to Canada even for 6 months does not reset the clock. US immigration deem that to reset the I94 (entry and exit form) you must leave North America completely.
However, there are no hard and fast rules that tourists can be guided by, the decision is completely down to the Customs and border official at the port of re-entry.
In 2021/22, we entered the US in November 2021, then near the end of April we crossed in to Canada with the intention of travelling from British Columbia right across to Nova Scotia. Unfortunately, the Canada we know so well has changed and although never a budget destination, has become very expensive compared to America. So much so that after 3 months we decided to see if we could re-enter the US when in Ontario.
We presented ourselves at the border crossing at Sault St. Marie and explained our case, quite expecting a refusal. We had to go to secondary for further discussions and as always, the truth supported our case and we were granted re-entry. Not everyone is so fortunate.
Now the second but, by entering Canada first you are governed by two constraints.
Number 1 is the seasons and weather, there are only a few months (April to October max) that could be considered tourist weather unless you either love the cold or are prepared to spend a fortune in heating. We spent May in a temperate valley near the border before climbing in to Alberta and still encountered snow and freezing temperatures in June whilst on the Icefield Parkway.
The second is your choice of accommodation. I honestly do not think there is the same choice of RV in Canada as there is in the US. They are there, whatever you decide you want, but you may have a more limited selection in any given location.
With regards to what you decide you want, A class, C class, travel trailer and truck, Fifth wheel, every one and their brother will tell you what they have is best but only you can make that decision. As I stated in an earlier post, we are very friendly with couples that cover all options and I am certain they will all say there are compromises in whatever you choose, as will we.
We have a mailing address in Montana which currently costs $99 per year. The address is a suite number, not a mail box. When they receive mail, they open and scan it and email it to you. You then decide if you want to keep that mail for later collection, have it forwarded at extra cost or disposed. The company that holds our mail also set up our LLC, but that is not a requirement, just convenient for us.
Our insurances are with Progressive, and they do seem very receptive to foreign nationals wishing to tour the US and Canada. You could always email them with what you intend.
I do not know who Jackiemac or the couple with the C class are insured with.
If you think that we can be of any further help, do not hesitate in following Jackie's advice and click the envelope to send a private message. We are always willing to talk on the phone if that is easier, as Jackie has already offered.
good luck with your adventure.