Pre-ground coffees sold in supermarket cans are almost always blends. The only exception I’m aware of at this writing is a canned dark-roast Colombia.
Many of the most widely distributed canned dark-roast coffees are ground far too coarsely for home espresso brewing. If you are a novice trying home espresso brewing for the first time, do not start with a canned dark-roast coffee ground for all-purpose brewing. The coarse grind will only lead to watery, under-extracted coffee and frustration. Several packaged dark-roast coffees are ground to espresso specifications, however. The labels of these true espresso coffees usually display language like "ground extra-fine for espresso brewing."
In style, pre-ground, canned espresso blends range from mild, sweet styles prepared in northern Italy to reflect classic Italian taste, like the famous Illy Caffe, to much more darkly-roast coffees with an earthy twist intended for "the Latin taste," as the language on the can usually puts it, to a 100% Colombian with dry, acidy notes vibrating inside the bittersweetness of the dark-roast flavor. These canned, pre-ground coffees can provide a helpful orientation to the range of experience possible in espresso-style blends.
Nevertheless, canned coffees are limited in several respects. First of all, pre-ground coffees, regardless of packaging, simply cannot deliver a cup of espresso as fresh as can recently-roasted whole-bean coffees ground immediately before brewing. Secondly, canned coffees can’t come to offering the espresso aficionado the variety that whole-bean coffees do.