Large pond just north of Hwy 407 in east Markham (York Region). A scope can be helpful here but not a requirement. When water is low can have good habitat for shorebirds in May/June and Aug-Oct. Great spot for waterfowl shortly after ice melts (late March, through April) and again in Oct-Dec (before freeze-up) - a great spot to stand and watch the geese come in to roost for the night in the evenings as the sun sets. Good spot for Cackling Goose - in the late fall there have been up to ~5,000 Canada Geese roosting here.

Waterfowl & some shorebirds. The fields around the north & west can be good at times too - great spot for nesting Willow Flycatchers (up to 4 pairs regularly)

Pond is accessible off the west side of Reesor Road but limited parking along the shoulder (and they're not very wide) - the road can be quite busy though, so caution is required getting in and out of the car! 
There is a paved trail but it is gated and can be stepped around that runs from the access point on Reesor, south about 200m and north about 300m. Not sure how accessible it really is for wheelchairs as it's often muddy, but should be passable.

The north trail gets to the far NW corner of the pond where there is a stream inlet, the south path ends at a small dam where the water flows out of the pond.

see notes in "About this location" above