Of the over half dozen subspecies of Canadas there are two big ones and one really big one. Moffitt and Interior I think the ones we often call Greater, I can't tell them apart, I have killed from Oklahoma to western Kansas as migrators. The really big ones Giant or Maxima are what Oklahoma stocked in the 1980s and what most of the resident geese are, though I am sure some of the other two species mentioned above are too. Those Giant Maxima resident geese are your best bet if your doing it on your own. I have targeted them successfully on some DFW lakes during the resident season when given the time to scout specifically for them. Even on high pressured areas. They leave the roost before sunup when hunters are coming in, then most hunters are done for the morning, off eating breakfast or lunch, or back home when the birds return to the lake. Several if not most Oklahoma lakes have big resident Canadas and the population is ever growing. Non hunting locals are usually very helpful for locating them. Spend a few days on one of those lakes with a good setup and you should not have a problem. If your looking for a guided hunt close to home for the bigger migrators I would look into guides in the TX panhandle to western Kansas and book a hunt later in the season for a better chance at the bigger subspecies in the mix.
"Onward up many a frightening creek, though your arms may get sore and your sneakers may leak. Oh! The places you'll go!" ~ Dr. Seuss