Straightforward case - all the required, strong proofs, no/not many red flags (like for example: big age gap, quick marriage without any visits), no criminal past or problems with immigration (for example, a refugee who was rejected and had to be deported). Also, if you were not married before/have been in a common-law relationship, that makes it more straightforward. If the sponsor was not sponsored him/herself in the past, then divorced to marry and sponsor another person, that's better. If the sponsor is living outside Canada, there would be an additional step to prove he/she would definitely come back to live there with the applicant. All of those things can delay an application more or less, and require it to have stronger evidence.
Thank you so much for such detailed answer. The only thing that I can see might not be exactly straightforward in my case is that I have visit really a lot of countries and in 4 of them spent more than 6 months, so I have 4 police certificates. Do you think it will take long for my background check because of that?