Yes it's true. You are deemed to have sold the stock on the day you transfer it to your TFSA. If you sell at a profit, you have a capital gain that you might have to declare depending on your personal tax situation (e.g. you may have some unapplied capital losses, etc…).
You have to sell your stock sometime, whether it's to liquidate it or transfer it to annother broker, etc… You're going to realize a capital gain (or loss) when you do this, so the fact that you happen to be transferring to a TFSA is irrelevant. Once the stock is inside your TFSA, any capital gains you realize upon selling the stock will be "tax free". However, you will NOT be able to use capital LOSSES incurred within a TFSA to offset your capital gains. Many people aren't aware of this.
The only exception to all of this is if you transfer your stocks within or between an RRSP.
You should have a chat with your financial advisor before you commit to anything.