Sadly, that usually doesn't work. You need an Incognito or private browsing window and/or an IP hider to change countries most of the time. Otherwise it keeps bouncing you back to the Canadian page as soon as you click anything.
It varies according to the resort level and then according to room price and availability. 15%-30% for the last few years (my mind was reaching too far back above) — Values get 15 and the expensive Deluxes get 30%, Moderates and lower cost Deluxes are inbetween. AP Holders and Fla residents occasional get up to 35%.
This was one of the original rumors out there, although I have yet to see the source of that information. I can say that Disney Tourist Blog did an update to their 2018 Disney World Free Dining post which can be found here. Based on what they are reporting, the more likely rumor is that based on the information released to South American travel agents the initial date that free dining would drop in that market is April 24th, 2018. This date is one which I have seen far more than the inital April 27th date. There have also been rumblings that it may be as early as April 23rd or as late as April 25th.
Personally, I would put my money on it coming out on Monday, April 23rd as the past several years it has come out on a Monday. Mousesavers has a great page which lists all the historical Disney World discounts which you can reference here if you want to check that information out for yourself.