By my experience, most likely those with Air Mail labels will be sent by Air Mail. The Canada Post Staff only look at the most visible labels. Once I put 2 different addresses on a single parcel (to different states in US), one is the large label printed on a white sheet, one is printed on the waybill (very clear but small) which is wrong. I called them and they told me it would be sent to either one. Finally it was sent to the right address which is on the white sheet. I don't think they will check the price on the parcels.
Andrew