Obtaining a Work Visa

[MsVee2]

I am a US citizen and I am trying to relocate to the province of Ontario. I have an appointment to receive my Nexus card in late July early August. My question is, do I need to be offered a position there before applying for a work visa? Am I allowed to work there before receiving my Nexus card? Someone please advise me on the process. Also, are there any companies that will sponsor?

Thanks for the help!