the suffixes are ötök, otok and etek for 2nd plural. why here kanalatok? is it exception?
Really? "-atok" is not listed as a version of the suffix? It does not feel like an exception. But it may be rare. Here, the word is "kanál", and the last vowel ("á") gets shortened to "a" when the suffix is added. But this is not the only word that does that.
kanál - kanalatok (spoon)
pohár - poharatok (drinking glass)
But there are other words, that do not shorten, and, still, they get the "-atok" suffix:
láb - lábatok (leg)
ágy - ágyatok (bed)
agy - agyatok (brain)
vágy - vágyatok (wish/desire)
kád - kádatok (tub)
tál - tálatok (bowl)
hát - hátatok (back)
Actually, the suffixes are -tok, -tek, -tök. And there can be a buffer sound between the word and the suffix, to ease the pronunciation. So, that is how we can end up with "-a-tok". It is the "-tok" suffix with the buffer sound "a".
You might also be thinking of conjugation of verbs here, where the suffixes are quite similar to the possessive ones, but not exactly the same.
To add to vvsey's explanation: the binding vowel is usually the same that is used when adding the -t suffix to the base noun:
- ház - házat - házam
- kanál - kanalat - kanalad
- könyv - könyvet - könyvetek
Doesn't work for nouns that don't have a binding vowel for the -t suffix, though: hús - húst - húsom