I think that this report is highly speculative at best. If I were the Lakers though I'd want as many reports out there as possible of teams being interested in Pau so as to help jack up the price. Do the Raptors really have the pieces to get a deal for Pau done? I don't really think so.
The best thing that the Raptors could possibly offer in return is Bargnani, a fairly attractive piece even in this terrible season he's been having, except that the Lakers covet the cap space they are going to have in the summer of 2014 more than anything. Unless Pau nets them players with small contracts or another true star at a position that makes better sense they won't accept players who have contracts extending past the summer of 2014.
Right now the only Laker signed for that long is Nash who is signed for a shade under $10 million for the 2014-15 season. Bargnani is also signed for 2014-15 at $12 million. You have to assume the Lakers expect to re-sign Dwight Howard so that means they have $20 million bookended for Dwight as well. This means they'd have $42 million committed to just three players. They'd have to really see Bargnani as a franchise type player to commit to that when they could instead be looking at having just $30 million committed which would allow them the flexibility to sign two players to max contracts without going over the salary cap. Not that the Lakers are extremely concerned about going over the cap but rather they want that flexibility because it is the best way to build your team. Unless Bargnani is really a part of their long term plans I don't see the Lakers wanting him return for Pau whose contract expires at the end of next season.
Calderon is a nice fit as an expiring deal and Kleiza's contract wouldn't really hold back a deal were it included for cap reasons but he's hardly an attractive piece on his own merits.
You might be able to convince me that the Lakers would consider something involving a valuable young piece like Valanciunas and the four years of affordable team control he offers beyond this season and as a trade chip plus Calderon's expiring deal and Kleiza for cap purposes but I don't see Bargnani as a centerpiece. It's a nice thought but he just isn't high profile enough to fit into the Lakers long term plans.
Maybe, and this is a real stretch, the Lakers could like Terrence Ross and his favourable rookie deal instead of Valanciunas but that seems like a stretch to me since Ross really wouldn't help them much right now, which is also a necessity for any assets they bring in.
It doesn't help that the Raptors have a conditional 1st round pick already traded and floating around (currently owned by OKC) which limits their ability to dangle a pick in any trade offer. This isn't to say they shouldn't have moved the pick for Lowry - he's the team's best player and offers hope as the team's long term plan at point guard - it just means the team has one less trade asset.
So this is more a case of the Lakers being really picky sellers and given the fact that they will almost certainly be trading the best player in any deal for Pau they certainly have the right to be picky. The only way I see the Raptors getting involved in any Pau deal with Bargnani is if there are more teams involved. For instance (and I don't know why they would agree to this but hear me out) the Cavaliers could send Varejao to the Lakers (his contract extends through 2014-15 but for that final season it is a club option and is slightly more cap friendly at a shade under $10 million) and then the Raptors get Pau sending Bargnani to Cleveland and Calderon and Ross to LA. This would never happen because Varejao is worth more than Bargnani at this point but this is an example of what the Raptors would need to get a deal done.
To me the team that makes the absolute most sense right now is Atlanta. They are pseudo contenders in the terrible Eastern conference and can offer the Lakers all the expiring contracts that they need. Josh Smith (a friend of Dwight's btw) fits D'Antoni's system way better than Pau does and is on an affordable deal that expires this summer. The Hawks have enough cap space that they could basically trade Smith straight up for Pau but they have no end of expiring deals that they could include to sweeten the deal and help match salaries.
Both Anthony Morrow and Kyle Korver would offer the Lakers the outside shooting they covet while playing on affordable expiring contracts. Throw either one into the mix along with Smith and you've got a really strong offer for Pau - one that I don't think any other team could match.