This is the link to the garlic white sauce at PMQTT. In my opinion it was great.
Norma, I'm sure that when you made this sauce, it was great, but, the chemistry is such that there's a pretty good possibility that on another occasion, it won't be as good. Cream cheese is one of the least stable cheeses you can buy. If you bring it anywhere near a boil, the chances are good it will liquefy. In recent years, they've been adding more and more stabilizers to cream cheese, so it's a little more hearty (some brands are more stable than others), but, for the most part, it doesn't like heat. If you add milk to the equation, there's a good chance the milk will curdle. Some people have a greater tolerance to watery and sour curdled sauces than others, but, generally speaking, curdled sauces are impalatable.
Cream cheese should never be used to thicken any sauce that will be heated. It's just too much of a crap shoot. Traditional Italian American alfredo is just half and half, parm (preferably reggiano), and butter. The parm provides plenty of thickening to the already slightly thick half and half. The butterfat in the half and half helps prevent curdling as well. In a pizza setting, though, the butterfat in the sauce can get a little heavy combined with the fat in the mozzarella. For an alfredo going onto a pizza, I'd probably go with a traditional bechamel, using flour, milk and a little butter for the roux.
JT, canning involves pretty high temps. When milk is involved it produces a lot of cooked milk flavors. The sugar in condensed milk acts as a preservative, requiring lower temps, so condensed milk is not so bad, but evaporated milk because of it's brownish tint and off flavors is kind of an acquired taste. Since alfredo is so easy to make fresh and about a million times better than canned, canned alfredo is one of those products that should always be shunned.