Went out to Sheep River today and it was amazing. Other than about 10m of snow in the final 2km, that you could still squeak through, it was perfect. If you're looking for 40km of no cars (20 out and back) you should definitely get out there before May 15th.
Lots of families out there too if you want to get the kids out.
Here's the Strava link to the route. The gate/closed section starts at Sandy McNabb.
https://www.strava.com/activities/5144966633
Link