Note that Ross, Johnson, and Valanciunas all have non-guaranteed contracts, and that only Lowry and Camby’s guaranteed portion is being shown.
Assuming the Raptors amnesty Kleiza, they save $4.6M, taking them to $60,357,040 . The current NBA salary cap is $58.5 million, meaning the Raptors would be $1,857,040 over the cap. Of course, once you consider that they have a mid-level exception available to them (which also counts against the cap), they are essentially well over the cap and would need to use the MLE of approximately $5M to sign a free-agent. The Raptors also have a bi-annual exception available to them, which is valued at $1.967M, and can be split across two players (unlike the MLE).
The Raptors can renounce the MLE, but in this situation it would make no sense to do that. For example, if through some transaction they free-up $7M worth of cap-space, then it would make sense to renounce the MLE and sign a free-agent for up to $5,142,960 (the $7M saved minus whatever they are over-the-cap by now). They also will have to deal with Lowry, which stands to make $6,210,000 unless waived by the 15th. If he does stay on the roster, the salary will balloon to $70,167,040 (just below the tax at $70.307 million), assuming a Kleiza amnesty, they’ll be at $$65,567,040.
Long story short, the MLE is the chief course of action Ujiri can take to sign a free-agent, and of course, trade. Even if he manages to waive Camby and he gets picked up by a team, it’s not going to create enough space to sign anyone beyond the MLE.