過去式 同 過去分詞ge分別??

Strictly speaking, both of the sentences are incomplete in terms of grammatical rules.

They should be:
(1) I saw this dress in Canada last year. (definite time in the past)
(2) I have seen this dress in Canada before.
I have seen this dress in Canada many times last year.

其實想講我在canada見過這條裙......邊個係正確.....??

I have seen this dress in Canada before. (正確)

I have seen this dress in Canada.