If he is planning on commuting back and forth, you might as well get him a Nexus card now because it will make it simpler.
Before he gets his PR, he can not officially live in Canada but he can come visit for up to 6 months. After that, there is no problem for both of you living in Canada and drawing US salaries. I do believe though that you must also file taxes in Canada if you are living in Canada but because of the tax treaty, they will not double tax you.
To start the PR process from outside Canada, you need to use these forms:
http://www.cic.gc.ca/english/information/applications/fc.asp and you must show your plans and intentions of moving to Canada once he gets his PR.
When he gets the PR visa, it is usually valid for a year from the time he did his medicals for his application so depending on how long the application took, he might have 6 months or less to land in Canada as a PR. He does not have to move to Canada right away though. He just has to arrive with his PR visa, do the paperwork and then he can leave again.
In order to apply for citizenship, he will need to spend 1095 days in Canada in a 4 year period. Commuting will not affect that since day trips don't count but if you take a one month vacation in the US, then it will delay his citizenship application by that month. The processing time for citizenship is 13-16 months right now.