The law changed because of Dr. Morgentaler. The Quebec appeal court overrode the jury’s “not guilty” snd declared him guilty; it was appealed to the Supreme Court. That court reversed the finding and ordered a new trial instead. The (Catholic, anti-abortion) minister of Justice offered a reporter bets that this unprecedented reversal would never happen again in his lifetime. The reporter should have taken the bet - the Quebec court reversed another “not guilty” jury verdict while waiting for the Supreme court.
(The stodgy traditional heirachy took several years to “get it”. Morgentaler was prosecuted and often found not guilty until one of his cases resulted in Canada’s abortion laws, like Roe v Wade, being found unconstitutional. Because of uncompromising political views, Canada has had no law whatsoever regarding abortion for 2 decades.)
IIRC, the Supreme court said substituting “guilty” for a jury verdict of “not guilty” is not allowed. A reversal results in a lower court being ordered to re-hear the case; see the trial(s) of Paul Morin for the murder of Christine Jessop. A not guilty was overturned due to improper instructions and a new trial ordered. At that trial he was found guilty. After another re-trial, he was finally found innocent.
Generally, today, a jury verdict of “not guilty” will stand in Canada. Not sure (IANAL) if that is embedded in stone. But basically, if you couldn’t convince 12 out of 12 the first time around, what are the odds you will next time?
And remember, appeals are over points of law; you cannot argue “I think the trial judge / jury decided wrong on the facts” - i.e. they should have believed witness A over witness B - unless the mistake is blatant. Facts are for the court hearing the actual witnesses to decide. Appeals just hear lawyers blathering about the law.
As for “speedy trial…” yes, people are indicted years after the fact for murder; but generally, unless it’s because important new evidence has come to light (i.e. we just got the accused’s DNA and found it’s a match) the prosecutor cannot sit on evidence they’ve known for a decade and then decide to charge you.