Depending on where you are trekking from (we live in Barrie) there are several Faires that are 4-5 hours drive from say the central point of Toronto. Sterling RF (outside Auburn, New York) is awesome, and so is Michigan RF (Outside Flint, north of Detroit). We have been to each of those at least one weekend each of the last 6 years, sometimes we visit twice. It's worth the drive and the cost of a hotel. We have also been hitting Great Lakes Medieval Faire in Ohio for the last 5 years, another great Faire.
These faires are not a one weekend go, they are permanent Medieval towns with wooden buildings. They usually run 6-8 weekends towards the second half of the summer into the fall.
If you want a REAL treat, head down to Maryland RF outside Washington. Hit it on a long weekend, as you will need at least two days to see the entire grounds. It's not for the faint of heart at a ten hour drive, but its been every year since 2004 for us.