Keep right.

In 1924, Prince Edward Island became the last province in Canada to switch from driving on the left side of the road to driving on the right side, joining the rest of North America. This change was prompted by the increasing popularity of cross-country automobile travel and the need for standardized traffic rules. The transition was relatively smooth, with few accidents reported except for two incidents involving horse-drawn wagons. Prior to the change, cars had been banned on the island due to concerns about frightening horses, but the ban was partially lifted in 1913 and fully rescinded in 1919. [Extracted from the article]