I hope you don't mind but I don't think I can keep this short.
On March 24, Shams Charania reported that Pascal Siakam had been fined $50,000 for arguing with coach Nurse in the locker room. The Raptors denied that Siakam had been fined but did not deny that the argument took place. Siakam had been benched in the fourth quarter in a loss to the Cavaliers (Toronto's ninth consecutive) and was rumoured to be unhappy about that and generally displeased with being blamed for Toronto's post-Kawhi struggles.
Gotta go further back in time a little before continuing on. Right after winning the Larry OB Kawhi Leonard and his team (Jeremy Castleberry, Uncle Dennis, maybe others) decided that the Raptors weren't strong enough to repeat. Leonard approached the Raptors about acquiring Paul George from the Thunder. Seeing what Sam Presti squeezed out of the Clippers you've got to assume the deal would've centred around Siakam, Fred VanVleet, and first round picks. Even if they made the deal they would still not be guaranteed that Leonard would re-sign and could make more demands (apparently Leonard's team thought the PG trade was a good starting point only and expected more). Raptors GM Bobby Webster and PBO Masai Ujiri decided to max-out Siakam and keep him and try to sell Leonard on the team improving internally. Leonard bailed but said Toronto were in heavy consideration, more so than the Lakers.
Siakam had a great fourth season and was nearly a consensus All-Star starter for the East. Nobody was complaining about him making $30MM that season. (Important to note that Siakam started playing competitive basketball when he was like eighteen! You can fairly take a few years off his career and picture him as more like a fourth-year player than a sixth-year player). Then the playoffs happened. Toronto swept Brooklyn and faced Boston in the second round. It was the first time he played in a series against a good team that schemed against him specifically. Siakam bombed that series, playing hard defence but averaging 15ppg on .382/.125 shooting. The series went to seven games because Toronto was still really deep and experienced and the thought was if Siakam was just slightly better they would've made the third round. This performance brought out a lot of critics of Siakam who started questioning whether he could be the guy.
If you compare Siakam's 2019 All-Star season to his 2020 "disappointing" season you'll see he actually improved in several areas (2P%, relied less on his 3PA, increased his free throws per, moved up to nearly 5APG) but didn't show the leaps-and-bounds year-over-year improvement he had over the previous two seasons. Toronto struggled in Tampa, lost more key players, and went into retooling. Siakam still got slandered online for not being what fans wanted him to be.
Is Siakam unhappy now? We don't know. When you lose nine straight and the ninth comes against a shit-tier Cavs team, you WANT your star player to be fuming. To me this isn't indicative of an unhappy player in the broader sense. He hasn't come out and said anything like he wants to be gone. Kendrick Perkins said on draft night that the drafting of Barnes meant Siakam was leaving. For starters, Perk is a hot take artist and kind of an idiot, but he is especially supportive of Toronto (like Charles Barkley seems to be) so who knows what his M.O. was. I think he was just referring to the story about the fine and taking that to mean Siakam wants out/hates Nurse. I think that's a stretch. Toronto's been good to Siakam and Barnes looks to be a multi-positional player like Draymond Green or Ben Simmons. I don't think he is a power forward to replace Siakam. He can play with him. But he's kind of a project too so I don't think it matters much this year what position he plays.
Trading McCollum for Siakam makes sense for Portland. They probably made an offer. Siakam running the floor with Lillard would be sweet. To me it makes no sense for Toronto. McCollum is going to be 30-years old this season (doesn't fit the core), he's a smallish guard (doesn't fit the type), and he's a Khris Middleton type complimentary star. Complimentary to who? This trade would make him our first option. It also stands to reason that re-signing GTJ for $17MM per year (trending that way) AND trading for McCollum is nonsensical. We DO need scoring but this move is an expensive and temporary way to address it IMHO. But what do I know?