CAN

Are the following settings possible in the uPD780701Y? If they are possible, what value would the system clock be at that time?

CAN bus timing parameter
Time Quanta                 1000ns
Synchronization Jump Width  3000ns
Sampling mode               Once

Yes, these settings are possible.
By dividing a 6 MHz system clock by 6 by setting BRPRS = 2, a 1000 ns time quanta can be selected. To enable this setting, set the data bit time to 8, the synchronization jump width to 3, and the sample point to 5 using SYNC0 and SYNC1.

Is the CAN specification that supports extended frames CAN2.0 (Bosch specification 2.0 part B)?

Yes.

Can transmission be automatically resumed when a continuous 11-bit recessive has been detected 128 times? Is initialization required?

Initialization is not required. When a continuous 11-bit recessive is detected 128 times, the error active state is entered and transmission/reception becomes enabled.

The manual of another company's product says "SAE-J1850 protocol (CLASS B)" compliant, whereas NEC Electronics' manual says "J1850 (CLASS 2)". Are these the same functions just with different names?

CLASS A to CLASS C are divided according to speed, and CLASS B is J1850. J1850 is further divided according to the communication system into GM-oriented (CLASS 2), Ford-oriented, and Chrysler-oriented (CLASS 2 + IFR). In other words, the CAN incorporated in the uPD780833 includes some of the CLASS B specifications.
Therefore, customers who wish for CLASS B may find not all the desired specifications are covered. As the CAN function cannot simply be replaced, be sure to clarify the specifications you require before using the uPD780833Y.