I suggest you double check as it gets closer to flight date to make sure it stays as A333 instead of A343 which AY normally use for HEL-SIN.
I bought my ticket back in June and at that time, AY website said A333 for my SIN-HEL flight next week (and I duly picked 4L as I don't like the throne seat). About a month ago I checked and it switched to A343.
I'm guessing it is due to delay in A359 delivery - A333 for SIN-HEL is supposed to come from routes that are supposed to switch from A333 to A359 by now.