It is not okay and not safe to eat canned chicken that was left out overnight once opened.
Even though the canned chicken is cooked it can still grow bacteria rapidly and make you sick.
If you've left canned chicken out overnight after opening it, then it should be thrown out and not consumed.
If you have leftover canned chicken it should be refrigerated within 2 hours of opening it to prevent bacteria from growing on the canned chicken.
Even if the canned chicken smells fine it can still be unsafe to eat.
Never leave any cooked meats or other perishable foods out of the refrigerator for longer than 2 hours as it can make you sick.
It is not safe to leave any cooked meat including canned chicken, cooked fish or other cooked meat out overnight.
Raw meats including raw chicken, beef, fish etc should not be left out of the refrigerator or freezer longer than 30 minutes or it can spoil and grow bacteria.
Raw meats will last 6 months to a year in the freezer but only a few days or so in the refrigerator.
Throw out any meat even if it was cooked if it was left out overnight or for a few hours.
The risk is not worth it and it can make you really sick and can even kill you in some cases.