Yes, I think new policies were introduced not too long ago that did give the CFIA a fair bit of teeth in terms of seizing products with traces of antibiotics in them. I do think that is a common cause of food being rejected at the border.
That being said, we don't always monitor for resistant organisms, as opposed to traces of antibiotics in the food. Canada does a good job, through CIPARS, of monitoring resistant pathogens that are circulating.