Upvote:2
Are you a permanent resident of the US? If so, you also qualify for NEXUS, and should have no problem: https://www.cbp.gov/travel/trusted-traveler-programs/nexus/nexus-eligibility ... just be sure to notify the NEXUS enrolment office of your change of circumstances once you relocate to Canada.
It sounds to me like you qualify now, and you will qualify once you move, so enrol now based on your current qualifications. Answer any questions they ask honestly. Your eligibility will, for now, be determined outside of your intent to immigrate to Canada.