In the last scene where Gil and Anne kiss on the bridge, watch closely and through the fog you can see telephone wires. I don't think they had those so early on.
Actually I grew up Prince Edward Island and have visited the home and area the story is based around multiple times(it is actually the home of Lucy Maude Montgomery the author of the anne shirly books, and am very familar with the history of the book and the area etc. At the time the books were written(same time the stories are based in) there were telephone wires on prince edward island(not telephone poles covered with wires like you see now) I haven't checked this slipup myslef so am unsure of what kind of glimps you catch of wires but I assure you during the time frame the stories are based in there were wires(maybe not telephone wires, but wires strung fomr poles(commonly referred to as telephone wires)) and if it was only a momentary glimps of some vague wires then it is very possible you would have seen them in that time frame..and if that is the case...this isn't a slipup.