Then you don't have any problem, you are worrying this way toooo early. Nurse LC-waiver(schedule A) now (more precisely, 3 weeks form now) are subject to EB3 priority date of 1/1/2002, so at this speed, you won't be able to start I-485 for three years when you will almost get Canadian citizenship in 3 to 4 years. EB3 immigrant visa number is no longer current for PRC born people and have a 3-year wait (we will know the exact retrogress trend next month). Think of an analogy, EB3 used to like marriage to US citizen, no wait for quota, but now, 3 years wait for priority date becoming current, compared to 5 years priority date wait for those who marry to GC holders now.
Chances are, you won't have this having two GC problem at all.