All the internal links were modified accordingly and old url is directing to the new one. I was of the openion that just by adding new parameters in the url does not mean it is a new url and would not affect rankings. Having said that, I see a drop in traffic after this change was implemented, about a month ago.
We do not have canonical tags. Am still not sure, adding parameters into the url is considered to be a new one or not, however, there is a drop in SEO traffic which could be either because of the changed url or low search volume altogether.