the stone henge on easter island.

First, to clear up this confusion, Stonehenge is in southern England, not on Easter Island. You're probably getting some mental interference from Easter Island's moai.

As for what this particular site in Manitoba is, it's hard to tell with the information currently available. This area is in the Border Trail Heritage System, which is many stone monuments to mark borders and commemorate various immigrant groups, but this doesn't appear to resemble those stylistically.

From above, at least, it looks like a medicine wheel. There are over a hundred surviving medicine wheels throughout the northern plains, predominantly in Alberta, where you can find the largest one: the Majorville Medicine Wheel. But Bighorn Medicine Wheel in Wyoming is perhaps the most famous. This map shows the location of many of the major surviving medicine wheels - you'll notice that this Manitoba site doesn't show up.

Not only is this site in Manitoba much further east than the vast majority of medicine wheels, it's also much large than the Majorville wheel. If your description is accurate and its composed of large, upright stones, that would also make it considerably different from any of the usual medicine wheel designs (it's also missing the usual radial patterns, but those could have been lost). The place is clearly being mowed regularly, so it's a known feature. Looking through the archive of aerial photos of the site, I'm suspecting it was built very recently. I'm only able to see photos going back to 2005 at the the moment, but you can see in that photo that an outer ring of young trees had recently been planted (also the road diverts southward onto a straighter path immediately after this as well; it used to come right up to the site). While it's possible that someone did new landscaping at an older site here, but at the moment I'm leaning toward the idea that this is a modern, privately owned creation because I'm finding no mention of this site anywhere. It's hard to imagine that something this large and well cared for is going to slip through the archaeological cracks otherwise.