You can, but you could be fined I think $230 dollars, plus get a criminal conviction for it. If you have a prescription for it, then no.
But yes, according to the new laws, if you are in possession of any marijuana product that was not purchased through the LCDB then that marijuana would be illegal.
But don't worry, nobody is going to fine you, there is nobody out there enforcing it person to person. Retail outlets however will ruin their chances of being granted a license by the government. The Minister even said on the radio that those who continue to operate today selling black market marijuana will go the the very Bottom of the pile of applications and would likely void their chance of being approved.
But the burden will be on the Crown to prove, beyond a reasonable doubt, that the marijuana was not originally purchased legally. You don't have to prove it was legally purchased.