Spellstrike does NOT say anything about overriding the standard attack of opportunity/casting defensively rules, so they DO still apply: if you cast a spell in a threatened area, you must either cast defensively, or provoke an attack of opportunity. The fact that you're delivering it via a weapon attack instead of a touch attack doesn't change that.
That being said, the rules for touch spells work in your favor, as far as casting out of melee, then moving in.
Pathfinder Core Rulebook, page 185, "Touch Spells in Combat":
In the same round that you cast the spell, you may also touch (or attempt to touch) as a free action.
Meaning you can cast out of melee as a standard action, move up to the enemy as a move action, and then make the touch attack as a free action. Since Spellstrike allows you to substitute a that touch attack for a weapon attack, the magus could deliver that weapon attack as a free action.
Note that you only get ONE free attempt (which MUST be used the turn you cast the spell), and you CAN still hold the charge if you miss, so you can try again next turn as a standard action.
And if you DM for some reason rejects that (explicitly legal) tactic, remember that you can also take a 5-foot step "before, during, or after" your other actions, so you could cast, then take a 5-foot step into melee range, too.