It is important to know that pool pump motors are not manufactured by the pump manufacturer; the motor will usually be manufactured by AO Smith, Magnetek, or Century Motor - all under the Regnal Rexnord umbrella.
Your pump's motor should have a label or faceplate on it which includes the information you need to replace your pump motor. The most important categories to note will be the horsepower (hp), motor frame (fr), voltage, and service factor (sf).
Some labels will provide you with a model number and it will usually be listed as CR or CAT. 1.5 HP - Full Rated Service Factor: 1.50 56Y Frame 115V / 230V 21.0 / 10.5 amps Square Flange (Face) Threaded Shaft Capacitor start All copper windings Automatic thermal protection Stainless steel threaded shaft Sealed ball bearings Cross Reference: 164654, 168454, 177081, 177476, 7-177476-20, C1307, EB858, 14728, 10-177476-20, 7-177081-24, 16-177476-28, 7-168454-24, 7-177476-26, 8-177476-20, 7-168454-25, 7-177476-28, 8-177081-40, 8-168454-25, 5KCR48UN2493X, B2858, SQD15FL1
When replacing your pool pump motor you should always replace the shaft seal as well. The shaft seal is a 2 part piece made of rubber, metal and ceramic and keeps water from entering the pump motor. It is located near the impeller at the end of the motor shaft.
Shaft seals vary between pumps so be sure to order the appropriate shaft seal for your pump.