The M7 (Size 1156) is correct for the 2000-UP Toyota Celica turn signal.
I know this a bit odd, but all 1156 bulbs, wherever you buy them from, are all two prong - they need to be modified for installation into the 2000-up celica.
If you take out your factory bulbs and inspect them - you will see that they came with a "nub" on either side at one time or another. Then that extra nub was removed so that it would fit into the socket correctly... Go look at your stock light bulb and see for yourself.
Install is simple, just choose what connector on the bulb that you do not want, and using a cement wall or curb to rub it off (or use a nail clipper to clip that "nub" off) Your bulbs will then fit perfectly.
This is the same technique that everyone uses to install their aftermarket 1156/M7 bulbs.
Here is another link concerning the 1156 Turn Signal bulbs...https://www.celicahobby.com/forums/ubbthreads.php/topics/16138/how-to-put-in-signal-bulbs.html