Do you think political parties do enough to vet their candidates before an election?
Yes.
Every party gives a very long questionnaire to each candidate for nomination. If the candidate has answered honestly and listed all of their social media accounts, there isn't going to be a problem. Problem is - they are politicians and they want that plum job with that gold plated pension - so, they "forget" to mention somethings.
Now, you ask why - since we have set election dates - can't the nominations take place a year, two years before the election date? It's because employers aren't going to want to employ someone who has already said they will be leaving about the same time that they have finally learned how to do their job.
The nomination approval committee for each political party is a little overworked vetting all of the candidates for nomination in all 338 constituencies. They can't check for stuff the candidate for nomination has lied about or has "forgotten" to mention.
Once the opposing parties know who is nominated, they can and do do an extensive investigation for any "dirt" they can use. CBC has an article on that:
http://www.cbc.ca/news/canada/newfoundland-labrador/election-liberals-ndp-mulcair-1.3244143 When it is an incumbent, the opposing party already has a book on the candidate - so - they only have to research a much smaller number of candidates.