I really can't answer that question. It's not often that I've found them to offer competitive odds on US sports and I do a lot of my US sports betting before they open for business in the morning. But on looking back through my database I find that there was a period when they were readily accepting bets of up to $3000, mostly on NHL and I didn't suffer any limitation despite doing rather well on those bets.
I have heard the odd story about them limiting big punters but never actually come across anyone who's suffered that fate at the hands of TAB.
I have heard the odd story about them limiting big punters but never actually come across anyone who's suffered that fate at the hands of TAB.