As you might have guessed, they are not the same. Depending on the producer, the whipping cream you buy at the store may be 100% whipping cream (including at least 36% butterfat), or it may include a tiny percentage of stabilizers, such as carageenan. If you want to make whipped cream, you have to add sugar or another sweetener and vanilla or other flavorings, unless you just want unflavored whipped cream (which no one really wants).
Whipped cream in a can is also based on cream. It is already sweet (generally sweetened with corn syrup, but some brands use sugar), and flavored with natural and artificial flavors (that are meant to mimic the vanilla you would likely add yourself). Aerosol-based whipped creams are always (we believe) lower in fat, and this is accomplished by using a blend of cream and whole, lowfat, or nonfat milk. Aerosol whipped cream also has a number of stabilizers to keep the whipped cream stiff. It may have vitamins added and it may have artificial color. The gas that whips it and shoots it out the nozzle of the can is nitrous oxide – also known as laughing gas.
Whipped topping (cue the villain music) is not based on dairy products, and is purchased frozen. It has many of the same stabilizers as the dairy-based creams, as well as natural and artificial flavors, and artificial color. It is sweetened with corn syrup and high fructose corn syrup. But the structure of the topping comes from water and hydrogenated vegetable oil (coconut and palm oils). In our opinion, the flavor does not resemble that of whipped cream, but there are many people who were raised on these whipped toppings and love them, so who are we to criticize?
In nutritional terms, light aerosol whipped cream has 15 calories in 2 tablespoons, and 1 gram of fat, which is saturated. The same amount of whipped topping has 25 calories and 1.5 grams of fat, which are saturated. It is hard to be exact about the counts of homemade whipped cream, because you may get more or less whipped cream from a cup of whipping cream, you may add more sugar than someone else, etc. But homemade whipped cream has about 50 calories in 2 tablespoons, and 6 grams of fat, 4 of which are saturated.
There is an Extra Creamy Cool Whip-brand whipped topping that features skim milk as its leading ingredient and light cream a fair way down the ingredient list, but, in our opinion, it also has very little flavor resemblance to actual whipped cream.