You will not find anything in writing about that because they are two separate countries. Canada has their own rules and the US has their own rules.
Be aware that the US can revoke your green card status at any time they believe you have permanently moved away from the US. If you have gained PR status in Canada and are living in Canada, they may well take that as a sign that you are living in Canada permanently. You would also have to continue to file taxes in the US, in order for them to believe that you have not moved elsewhere on a permanent basis. You can also not be outside the US more than a year at a time. Better if it is only 6 months. Years ago I knew people who kept a green card alive just by going to the US every 6 months but I think they are watching it more closely now where you are actually living.
In Canada, the rules are that you must be in Canada at least 730 days in any rolling 5 year period. They don't really care if you have a green card in the US. If you stay 6 months in each country, you would be able to keep both PR's alive but in order to do that, you would have to find a job where that works and you would have to find housing where that works.