No, you can't cast a spell with your extra action from haste.

Despite including an attack as part of the cantrip, all cantrips use the Cast a Spell action, like any other spell. Haste's options are limited as you indicated, and Cast a Spell is not among the available options.

But... Divine Smite!

The paladin's Divine Smite feature is not a spell, despite being fueled by spell slots. Paladins have other kinds of smiting that are spells, but Divine Smite is not. It triggers when you hit a creature with a melee weapon attack, but does not take any sort of action; any melee weapon attack that hits will suffice.

Wizard A gets 3 weapon attacks

Tenser's Transformation says:

You can attack twice, instead of once, when you take the Attack action on your turn.

So, when the wizard uses their normal action to Attack, they get to take 2 attacks (per Tenser's Transformation).

When they use the special action from Haste to take the Attack action again, however, they only get one weapon attack because Haste specifically limits the number of attacks to 1.

[The hasted creature] gains an additional action on each of its turns. That action can be used [...] to take the Attack (one weapon attack only) [...] action.

This is a specific restriction which overrides the number of attacks granted by Tenser's Transformation just as it supersedes the same exact ability as granted by Extra Attack.

Thus, a hasted, tenser-transformed wizard gets three weapon attacks.