The only advantage of cruising in January is that it tends to be slightly drier. October/November is still "rainy season". It does tend to rain every day in the tropics, but January can be a little drier.
However, you may find better rates and availibility by cruising in October/November.
We did the canal the last week of October/first week of November and yes it is the end of the rainy season, so we did encounter showers while traversing the canal. It was a welcome relief from the hot sun. We did a San Juan to Acapulco one-way trip on the Vision (RCCL) and thinking back it was a wonderful cruise, so relaxing. Although we did not have it this trip, a verandah cabin would be a nice benefit.