It depends upon where you depart and where you arrive.

Departing out of or arriving into high traffic areas, you can usually
expect a canned routing. This is to help the understaffed controllers
keep the flow moving.

It depends upon what lies in between the departure and arrival points.

You will not get a routing along the Lake Michigan shoreline during
AirVenture. You can overfly or underfly the CBAS VFR, but IFR they will
send you around to the west and south.

The "computer" will not accept your routing. This is one of those secret
things that a controller will tell you when you inqire as to why your
"Cleared as filed" flight plan is being amended. He/she doesn't know
why, it is due to something further down the line towards your destination.

Sometimes you can successfully argue to stay on your filed route with
the caveat that you will have to negotiate with each and every
controller at each handoff. Each will try to amend your clearance, just
like the first one. They, too, will not know why the "computer" will not
accept your routing.

Do not accept an amended clearance without first looking at it and
determining if it will adversely affect the safety of flight.
Does it add time and distance affecting your FAA mandated fuel status?
Does it place you over water without floation gear?
Does the amended routing place you in an area of adverse weather?
You do not have to accept their routing, you can propose alternate
routes more to your liking.