|Heavily processed swan photo to bring out feather detail|
Then I got a better look; what you see through the viewfinder, even with the roughly binocular-equivalent magnification of a 250mm lens, isn't as much as one sees with the picture tossed over the width of the monitor. (Not unless you've got a really teeny monitor.)
The swan on the right has a yellow loral patch; that would, if I were feeling very, very rash, mean "Tundra Swan!" but I know that in Ontario, there are some Trumpeters with yellow lores. It's big and it's really yellow, though, which is not how Trumpeters tend to go; trumpeters with yellow loral spots tend to have faint, vaguely round spots, not the largish bright patch seen here. Neither swan has yellow feet, so I know they're not leucistic. (The feet being about the only reliable way to tell with swans, since their plumage is already white.)
The swan on the left has, in another photo,
|Over-exposed, but see that bit of red in the gape?|
Some field guides will suggest Tundras have lighter, more delicate feet than Trumpeters; neither set of feet looks especially delicate, and neither looks banded, which argues against Ontario Trumpeters, most of which get banded. Size is generally a useless character without another swan for reference, and both of them are way fluffed up, which will make them look big, and convolved for preening in the bargain, so neck posture characters are no help. I have no ability to tell if they look proportionately long-legged, which goes with Tundra. The Goldeneye duck surfaced in the open water between the swans in one photo (not shown!) isn't much help, either, since it's in view from its own port quarter and preparing to dive, not ideal conditions for being used as a ruler.
So I'm down to "Not all tundras have yellow loral spots", "the upper margin of the beak is a smooth curve, rather than showing the widow's-peak style point typical of Trumpeters", and "eyes notably distinct from the beak, as per Tundra, rather than subsumed in the rear margin, as per Trumpeter".
So if I had to say something, I'd say Tundra. But I'd much rather get a swan expert to do it.
[I originally wanted to do single-exposure-HDR to bring up the feather detail in that first photo, but would need to know what I was doing rather than pushing "next" buttons to handle the "white bird on ice on a sunny sunny day" case, so the photo provided has had the exposure dialled way down as though it were not a sunny day at all.]