Could as well vs may as well

Anonymousare those expressions interchangable?

In some cases.

What about the sentence I wrote? Could the be used with the same meaning?

There's no context, so the meaning is unclear.
(There's no apparent reason why they could not have the same meaning.)

Let's assume that two friends are coming back home from a party. A says: I could ask my parent to drive us home. B replies: We may/could as well go by bus.

In this case, "We may as well go by bus" has a negative implication, in my opinion. B would prefer not to ride with A's parents.

On the other hand, "We could as well go by bus" is simply an alternate suggestion.

Sometimes "may as well" is used sarcastically.

Shall we go to Vegas? (reply) We may as well go to the moon. (I'd rather go to the moon.)

"Could as well" for a "Plan B" sentence is absolutely wrong.