If you were to become pregnant while on LTD, does that end your LTD payments? If it does, would maternity leave compensation be the substitution, or is maternity leave only available if you are working leading up to becoming pregnant?

You would unfortunately have to check your LTD policy as each policy is different, so we cannot say for certain.
Typically, maternity leave benefits from the government EI program require active work hours within a year before leave, so if you've been on LTD for an extended period, you may not qualify. However, I'd suggest looking into this more through the government website, here: https://www.canada.ca/en/services/benefits/ei/ei-maternity-parental.html

If you run into any issues with your LTD, please contact us again and we will help.