Gmail Migration - New Support Content

I have a question about the Gmail migration and existing Telus email account names vs aliases.

With the Gmail migration, my understanding is that it basically means I end up with a new Gmail account where my username is my old Telus email address, and Telus arranges migrating over my existing data (inbox etc)

I'm not sure if this is same for everyone or just an artifact of having a very ancient Telus email account (long time internet customer), but my existing Telus email account name is a bunch of random alphanumeric characters assigned to me, way back when e.g. of the format "[email protected]"

of course, I have an alias of the format "[email protected]" which I use for everything, including webmail login etc. I don't really even remember the alphanumeric username without looking it up.  Same goes for several family members on the same home internet account

So my question is this:   does my new Gmail account username become my hard to remember alphanumeric "actual" email account name, or my preferred alias?     If the former, then before migration should I rename my account? (looks like there ability to rename in myTelus account page). Or do I have a choice at time of migration

Before scheduling my migration I want to make sure what my new username on gmail will be. 

thanks