Agree with Twill. I'm from Ontario myself, and you just can't find this Tejano-style Tex-Mex grub up there at all. Hell, it's hard to find good Mexican of any kind up there.
Barbecue. You may find good Mexican in other cities around the US, but you won't find this particular style of barbecue anywhere else, so eat it up while you're here. If you've got wheels, head out to Lockhart/Luling and sample them all. There are plenty of in-town suggestions for barbecue as well, though I think they're in a second tier.
The other thing to consider is getting some good Southern-style grub like meat'n'three.
I checked out a couple of your posts from the Ontario boards, and I think you'll find that Austin has a preponderance of really good Mexican food offerings–some with an Americanized slant, but a number that have pretty authentic south of the border fare. Honeybee has already mentioned Angie's which has some of the better homemade corn tortillas in town. If you're open to exploring some places off the beaten path, you do well to check out MPH's comprehensive series on the East and Southeast side of town, which you can easily find by searching "Tex-Mex on Austin's Southeast and East Sides"
You're best bet–as mentioned elsewhere–to focus on a particular type of food (Mexican, BBQ, etc.) and use the search this board function.
Some additional parameters would be helpful, as well as the part of town you will be in and if you will have access to a car.
Chef Rachel gives you some suggestions for the most popular places in the area. If any pique your interest, you may want to search for them individually on this board (somtimes popular does not equal good).
I suggest consider the following places. They are not necessarily the most popular places in town, but I like the food and they are not so off the beaten path that they will be hard to find.
House Park BBQ (lunch only) on 12th and Lamar
Sam's BBQ on East 12th
Angie's on East 7th (breakfast/lunch- only go there for the carnitas tacos, the rest of the food is average)
Whole Foods on 6th and Lamar (simply for the experience of it)
Tony's Southern Comfort on East 6th
Casino El Camino for a burger
El Chile on Manor
Uchi on Lamar for upscale sushi
Enjoy our town!
For a lovely sit down, somewhat fine dining restaurant, I highly recommend Cafe Josie. Great ambiance, wonderful food, especially good sauces. And, right next door is a great little cafe/ lunch spot called Portabla. Their soups are amazing! For BBQ, you definitely need to hit The Salt Lick - it's world renowned. South Congress Cafe is a cute spot with a pretty diverse menu. Mars on South Congress is always great. And, finally, there is always Whole Foods Market. Not your typical grocery store AT ALL. It has 5 different restaurants within the store itself so there are tons of options. But, quite honestly, I think that the best food that you will find in town is Mexican food. If you are willing to venture out, Fonda San Miguel is absolutely fabulous. A little pricey, but, if you get a chance you should at least go there for dessert. Their Crepas de Cajeta are TO DIE FOR. My favorite dessert ever!
Also, if you are on a budget and/or want to eat late at night, there are two 24 hour places that are good ol' Austin standbys: Kerbey Lane Cafe and Magnolia Cafe. I think everyone who lives in Austin has probably eaten at these places at least a gajillion times. They serve breakfast 24/7 and lots of other stuff that will do the trick in a pinch and won't cost you an arm and a leg.
Hope these help. Enjoy your visit!
If you have specific preferences, you might want to try a search of the board. This conversation from a couple of months back (and the embedded links) should lead you to a few suggestions, no matter what you may mean by "American grub."
If nothing strikes your fancy, you might get results if you post a specific description of what you're looking for and how that's different from what you're seeing. Enjoy the visit.