If the digits can be any number from 0 to 9 and there are no restrictions on a number being used more than once then you have 10 choices for each digit and 26 choices for the letter.
The total number of possible codes is 10 x 10 x 10 x 10 x 10 x 26 = 2600000
If you include 0000, ten thousand unique four digit codes are possible.
1000
8 digits.
10,000
Since our postal codes are order like this (letter, number, letter) (number, letter, number) the result would be 26x10x26x10x26x10=17,576,000. There are 17,576,000 POSSIBLE postal codes in Canada.
900 ,999 ,909
100,000 - Every number from 00000 to 99999.
10*9*8*7*6=30,240
As far as I can tell, all 5 digit numbers are potential zip codes, so there are 99999 + 1 potential zip codes, or 100,000. Many of these are not actually is use.
24
5
With no other constraints, 26 x 26 x 26 = 17,576 possible three-letter codes.