Speaking to a Holyrood committee, he said tunnelling would be cheaper than the bridge suggested by Boris Johnson.
The number of Scots in work jumped by 37,000 in the run-up to Christmas, official figures show.
Boris Johnson told MPs during Prime Minister's Questions that the people of Scotland "voted decisively" in 2014 to stay in the UK in a "once in a generation choice".
Ex-justice secretary Kenny MacAskill - and newly-elected MP - said a longer wait is 'no bad thing'.
Scottish party leaders delivered their New Year messages ahead of the start of a new decade.
The latest economic figures show Scotland has returned to growth, with GDP rising by 0.3% in the last quarter.