TN holder going back and try to work for same company in US

Hi,
I've been on a TN status visa for the past three years, so is my wife( we are both canadians). We've decided to go back to Canada to raise our family. The small company we work for is willing to keep the working relationship going. As I was reading on previous post, it seems like working for a US company from Canada is not too much trouble.
I already have a Social Security Number. Should I still get ITIN number? Will my SSN stay valid?
The intention would be to keep my actual employee status, is that the best way to go? We are a design firm that has an Errors and Omissions policy which makes it very complicated if I was to be a sub-contractor to the company, so I'd really want to stay as an employee.
Which specific forms should I fill?
I'm still in the US for one month, leaving end of January.

Please advise, thanks

Louis

You need to be a CDn employee, with Cdn withholding and payroll tax.

You are not to get an ITIN, since you have an SSN.

You need to negociate with your company, and then THEY need to set up Cdn payroll for you.

Your SSN is yours to keep for life even if you change to a Canadian employer once back in Canada.