I have not heard anything about the Embraer 170/190 series being more rough (turbelence-wise) than any other mainline jet aircraft.
However, turboprops are a different story...
For a short YYZ to LGA flight, you shouldn't have much trouble turbulence-wise (on any jet aircraft).
Since you are traveling as a couple, I would actually recommend the Embraer. This is because on the Embraer the seating is 2 by 2. So you actually will get two seats to yourselves! There is also a better lavatory to passenger ratio on the E170 and E190 than other mainline aircraft.