My take on it is that base (SR and SR5) versions would probably use an A25 series engine, all others except TRD Pro would use some form of the T24 series, while the TRD Pro would use the V35 series.
The SR and SR5 would use a hybrid version of the A25, like what is used in the Crown, as it is a longitudinal engine. This would help maintain a high CAFE rating. Power would be in the 175hp, 170lb-ft (both +/-5) range, with maximum torque around 3500 rpm.
The other trims, outside of the TRD Pro, will probably get a non-hybrid version of the T24 series. I would speculate about 270hp and about 320lb-ft., with max torque around 2000-2500rpm. I would look for the 6-speed manual in these trims. I'm tempted to speculate that the Limited trim would feature a hybrid T24 with about 290-310hp, and possibly be an option on other mid-level trims.
The TRD Pro, in order to compete with the Ranger Raptor and Colorado ZR2, should come with a V35 engine. This one probably won't be hybridized, and power levels mirroring those of non-hybrid Tundras. I wouldn't be surprised if there was a manual transmission offered.