Sure they can. Rashford and Greenwood were for long parts of their (short) careers considered strikers. Many people still see Greenwood as one. They aren't natural wide players, Rashford closer to than Greenwood but he's a inside forward. Essentially go back to the days where strike partnerships were commonplace and both would be used pretty exclusively in a front 2, since neither really suit being a lone striker just yet (or ever). In a front 2, can't think of a more perfect set up for them. Rashford and Ronaldo can rotate, Greenwood and Cavani, and then Bruno with Sancho to be the creative option in the front 3. Can switch it between a 3-4-1-2 or a 3-4-3 at will and give the opposition different things to think about, and it relieves those attackers of defensive responsibility they have out wide in a 4231 which they are frankly awful at and a big part of the overriding issue anyway.
Personnel wise, a 343 or 3412 has huge potential for us. We can't fit all our attackers I'm a 4231 anyway, as it's horribly unbalanced, so this is our best chance and actually has a better chance of getting them all in their best positions. From there, it's on Ole to manage it properly. There's no reason why they can't all be rotated effectively. Can even play Pogba in midfield with a better success chance as he has a back 3 behind him, not just 2 CBs. In terms of style of play when using it, there's no reason it has to be defensive or attacking. Up to the coaching for that, but nothing to do with the formation.
Unfortunately I expect Ole will likely overplay Bruno and Ronaldo as usual, but the thing is it doesn't have to be that way. Ole's coaching is relatively negative but again, doesn't have to be that way. Another coach could implement a 3-4-3 perfectly. But if your dream is playing 4 of Bruno, Sancho, Rashford, Ronaldo, Cavani, Greenwood regularly, then IMO its never going to work well enough.
