OTs have a very similar outlook and pay to SLP. It is also really competitive, but I would say a bit less so than SLP, in some ways. I applied to 3 schools for SLP and 3 for OT. For those schools OT acceptance rates are like 6%-11% and SLP are 9%-13%. Despite that, it seems like lower GPAs are accepted for OT. McMaster did interviews last year for people over 3.5 GPA, I think.
CDA is different. The job outlook is pretty good, but it isn't a nation-wide career yet. I don't think it's very common to see CDAs outside of Ontario and Alberta. They make around $20/hour.
OT applications were due in January. I think some CDA programs are still open, but they've started acceptances already. And backups are great, but it's worth working on getting into SLP for a few years, if it's what you really want.