So mostly your decision should be based on environmental impact of canned versus frozen since it appears the nutritional content is about the same. However from my reading of labels of canned foods, the sodium content can be much higher than plain frozen vegetables and added sugar may be a problem with some products such as yams.
See Fresh, Frozen and Canned Vegetables: Is There Really A Difference in Nutrient Levels?
According to a number of studies, fresh vegetables lose about half of
their vitamins in just a matter of days after being harvested, if not
properly chilled or sustained. And even after you refrigerate the
veggies they still lose at least 50 percent of their nutritional value
in about a week's time.
So unless you and your neighborhood rabbits are eating the stuff right
out of the ground, you're going to lose quite a bit of the potential
The good news, according to Amy Jamieson-Petonic, a registered
dietician and spokesperson for the Academy of Nutrition and Dietetics
based in Cleveland, is that there is actually very little difference
between fresh, canned or frozen vegetables, so consumers shouldn’t
blindly plunk down extra money for fresh produce.
See also this article from Silgan Containers Canned Foods: Frequently Asked Questions which provides some information about canned foods as well as this page from the company about canned foods and sustainability.
I am not sure that there is much energy difference between canning and freezing vegetables. Both must be processed though several stages of preparation before either being canned or being frozen.
However once canned, canned vegetables require much less energy since they can just be stored. Frozen vegetables require continued energy use to maintain being frozen. The difference in energy is when being stored and when being transported.
As you pointed out cans may be recycled and I know that I do. Plastic will not.
This article comes to the conclusion that canned versus frozen so much as production impact are about even. Buying Frozen Veggies Versus Canned: Which is Greener?
All told, for 450g of corn, the can totals out to be 2,306 kcal, while
freezing requires 2,272 kcal. Pretty much a dead heat...Except when
you consider that you can store the can in the cupboard without any
additional input of energy.
Food, Energy & Security assumes that it's going to take about 120
kcal/month of energy to store each package of frozen corn. That means
that if that corn sits around in a freezer for more than about 100
days, the very slight advantage it has over canned corn is gone.
The verdict: In terms of energy usage in packaging and processing,
freezing and canning come out pretty even.