Blake (22) is set to leave New Zealand rugby in a couple of weeks and has signed a contract with Edinburgh, which plays in the Pro 12 competition for top Welsh, Scottish, Irish and Italian clubs.
It is the club Highlanders back Phil Burleigh joined this year.
With Scottish grandparents on his father's side, Blake qualifies as a local player and could conceivably play for Scotland.
''I was off contract with Otago and with my grandparents having emigrated from Scotland, I can get residency and can go as a local player,'' Blake said.
''Things have not been progressing much here. I had one year with the wider squad with the Highlanders but had nothing for next year so I thought I would take on this opportunity.''
Injuries in pre-season have hindered Blake, who was the only player from Otago to make the New Zealand Colts in 2012.
He suffered an elbow injury last year in the final warm-up game and picked up a knee injury before Otago's season this year.
''Those injuries really hurt. You don't play those first few games of the season and it is pretty hard to impress Super rugby coaches.''
Blake was in the Highlanders wider training squad in 2013 but did not get on the paddock in a forgettable year for the franchise.
He also spent three weeks with the Chiefs last season, covering for injuries, but again did not get any playing time.
Being classed as a local player, Blake could play for Scotland immediately but said any talk about that was off the mark, and he was just wanting to get on the field and play.
''That hasn't really been discussed. I did it all through Scottish director of rugby Scott Johnson. I just want to get over there and play some games.''
He had signed a deal until the end of the northern season, as he was sorting through his residency issues, but was confident a longer deal would be completed at a later date.
Southland and Highlanders flanker John Hardie is believed to be heading to the same club after the next Highlanders season. Hardie also qualifies as a local player through his ancestry.
Blake has six papers left to graduate in accounting and finance from the University of Otago and will do some papers through correspondence.
He played 20 games for Otago, after making his debut in 2012.
He was never a permanent fixture in the side because of injuries and competition for places.
With Blake gone and TJ Ioane looking elsewhere, Otago will have to find some new loose forwards next year.
Spence (23) has picked up a deal with the Bordeaux club as a medical cover and will join the club immediately.
French winger Sofiane Guitoune is out injured, so Spence has signed to play in the French Top 14 league.
He was training with the Otago sevens squad last week but is now moving back to the 15-man game.
Spence first appeared for Otago in 2011 and has played 39 games for the province, mostly in the midfield and also on the wing.
He made the Highlanders wider training squad last season after Richard Buckman was promoted to the main squad, but did not get on the field.
