Is there a limit on the dollar amount of a personal check?
Because of the way checks are processed, you can't write a check for $100 million or more:
The field used for 'amount' has 10 digits, so anything at/above 10^10 cents (which would require 11 digits) can't be processed, at least not by normal means.
Like the old American Express commercial: "no preset spending limit".
It is really up to the bank(s) in question how big a cheque they are willing to honour.
A larger amount would likely be held longer by a receiving institution to ensure that it cleared properly, but nothing written in law (in Canada, that I am aware of).
Many businesses will request that you get a bank-issued check for large amounts of money. The exception is often in cases where you're not going anywhere: you can write a 50,000 check for a deposit on a new house, and you'll never have a problem, but a car dealer will probably request a counter check for the same sum.