There are two kinds of aspects to building a canal.
- The engineering aspects. Is it possible to build a canal from A to B? What would it cost? How long would it take? What physical obstacles are there and how could they be circumvented?
- The political aspects. Is there political will do it? Is there relevant political opposition? What are the geopolitical implications?
The engineering aspects are questions for civil engineers, not political scientists. They are off-topic here.
The political aspects are of course relevant here.
Unfortunately this question does not mention if it is talking about engineering aspects or political aspects. It just asks: "Is it possible?". So if I would reopen this question, I would have to put it on hold again as "unclear what you are asking". And even if we assume that it's only asking about political aspects: These would vary greatly depending on where you want to build a canal. A comment by the question author mentioned Africa as a possible example of a region which could benefit economically from building more canals. But Africa is large and diverse. There are many different countries in Africa with very different political situations. So it would have to be put on hold for being "too broad", too.
Further, the question seems to be based on a faulty premise. The author assumes that no government is doing it, when there are in fact plenty of examples of artificial canals or natural rivers being modified to allow larger cargo ships. The author either did not know that (which would make the question unnecessary now that they know) or we didn't understand what the author actually meant with the question, which is another reason to put on hold as unclear.
tl;dr: In my opinion, the question needs a rewrite by the original author before it can be reopened.