There is a 600ft walkway between terminal C and D. *If all goes well*, you can certainly make the 1 hour connection on LGA. Is it the ideal situation ? no...
A few things to consider:
Customs: Assuming you are leaving YYZ, you will have pre-cleared customs so one less thing to do in LGA.
Time of day: If at all posssible, choose the earlier part of the day for travel. There is a morning rush once the airport opens and a peak time around 5-7pm with the departure of overseas flights. Any delays get compounded over the day. LGA is bad for that and will implement ground delays or ground stops if their traffic volume is too high. This usually happens some time in the afternoon so if you go early in the day, you can mostly avoid that.
Wort case scenario: check and see if there are other flights LGA-MCO later in the day in case you do miss yours. Nothing worse than spending the night in LGA because you just missed the last flight out. Having said that, there is no guarantee there will be room on the next flights but at least there is the possibility...
I am in the same boat as you. Up til yesterday, I had a 3 hour connection in LGA which was great. Lots of wiggle room ! Yesterday I got an email saying my inbound flight YUL-LGA had changed and now I have 1h45misn which I am not crazy about. I travel end of February so the weather is most definately a huge factor.
Here's hoping for good weather !
