The problem with acquiring pitching via trade is that you have to give to get. With limited high-value trade options on the major league roster, trading for high-upside pitching would likely mean dipping into the Jays’ prospect pool – which would not be the first choice of many writers (including this one).
Of course, pitchers can also be acquired via free agency. The positive is that they only cost money. But the negative is that the good ones can cost a lot of money. And many (most?) free agents are at the declining stage of their careers, which is an imperfect fit for a Jays team who will likely be rebuilding in 2019 (and possibly 2020)
But there is a third option.