Some cases you can peruse to see how the Court has reasoned this sort of issue in the past:
Ramsden v. Peterborough [1993] 2 S.C.R. 1084 - a case not even dealing with political speech, but whether a ban on postering on public property constituted a violation of s. 2 Charter rights. Spoiler: it did.
Beaumier v. City of Brampton [1999] O.J. 4407 - Whether placement of a sign critical of an insurance company and subsequent charges constituted a violation of s. 2 rights. Again, the Court found that the bylaw was overly broad and failed to meet the s. 1 test as it did not have a minimal impact.
Obviously, if the Court believes these cases to be violations of fundamental freedoms (as they were not even political speech), any law prohibiting election signs would be doomed.
I'm not saying the signs aren't annoying in some way, just that they cannot be banned during an election cycle.