BTW, it's 75-300, right? Not 70-300.
75x1.6 is 120. Personally, i think it's way to long; esp for the tea ceremony. You've got to shoot from the neighboring block to get the whole scene in. (Anyway, it's usually crowded during the tea ceremony. Step back a bit, and some aunty/uncle will block the view.)
If you're on a budget, try the 3rd party 19-35 (<$400). If you're financially sounder, try the 16-35 (~$2.2k), the 17-40 (~$1.2k) or the Sigma 14mm (~$1.2k). The 15/2.8 fisheye can be a good wide angle alternative too, coming in at ~$1k for the Canon one.
A 50/1.4 is great too; try it at f1.8, ISO800. Should be able to get great available light candids of couple and friends at wedding reception.