Yes, you can apply for a US Work visa. However, if you are being sponsored under the Family Class for your PR, you will not get that if you leave Canada.
If you've applied under CEC or FSW, then you can go ahead with no real issues that I know of.
I called IC and got the answer. Except applicants sponsored under the Family Class, a person can leave Canada and work in any country while PR is being processed.
I called IC and got the answer. Except applicants sponsored under the Family Class, a person can leave Canada and work in any country while PR is being processed.