I have moved to Canada with my wife who is Canadian and we are in the process of filing for a spousal visa with a work permit. I own a marketing business that is based in the UK. Am I allowed to get Canadian clients that pay me into a UK account?
No - you can't. This will be classified as working illegally and means you'd be in violation of your visitor status in Canada. You require a work permit to engage in any work within Canada that involves Canadian clients (how you are being paid doesn't matter).
Until you become a PR or obtain an open work permit, you'll need to stick with non-Canadian clients.
