I don't remember any proposal to move the border in favour of Morroco before the independence : if there was one thing on which both FLN and France agreed, it was that the integrity of colonial Algeria's territory had to be maintained.
There was,
post-independence, a somehow murky attempt by French diplomat to support Morrocean's claim on Trinquet Line being a temporary border and critically on western Algerian territories. But it was half-assed at best, some tentative to divide and rule before Boumediene's coup and while autogestion-like attempts by Ben Bella could be seen as a threat on post-colonial French interests.
I can miss something, and I'm not the most knowledgable person on the matter. But to imply Morroco did supported FLN is really, really hard to proove.
There's exemple on how the fifth wilaya's bases within Morroco were crushed by French forces up to the end of the war.
Morroco seems to have a more murky attitude : not actively fighting FLN bases and troops, but not really defending them either, trying to get benefits from each sides.
Which brings back to the point : Morrocean and Algerian elites were quite different, and definied themselves (especially in Algerian Atlas) by comparison with their neighbour, especially with a Morrocean identity that was definied with the dynastical reinforcement of Alawites : summarizing it roughly, a quite identified state from one side, and from the other, peoples that didn't identified themselves as part of it.
Of course it's more complex, and Morroco could have absorbated Tinduf at some point in the XIXth without too much trouble. But by the 60's, westernized conception of state came by, and colonial borders were an important political matter (it's interesting to see that Morroco, having kept more pre-colonial features when it came to its political ideology, was really opposed on this regard with the more modernist take of GPRA)
Point is, sorry to get this long, that Morroco itself couldn't have taken by his own to unify Maghreb as more it would have attempted so, more you'd have a reaction from Saharian (and Coastal evenmore) populations east of their IOTL territory. Different elites, different references.
Now, could Morroco becomes sort of PanMaghrebi leader; comparable in the region with Nasser's PanArabism?
Eh... I could see where it could come from, but for reasons aformentioned above, I don't think so.
However, and that might be an interesting twist, with a more integrationist (territorialy speaking) French colonial policy : Morrocean dynastic/imperial elites could have fueled a PanMaghrebi ideology more efficiently that if it was incarnated by a state.
Let's imagine that, for some reasons (Alawite/Saadian conflicts goes really bad and end with territorial desintegration?), most of IOTL Morroco, Algeria and possibly part of Mauretania are treated by the colonial power as a whole : maybe not a
départementalisation, not at this scale, but some sort of territorialisation equivalent to AOF/AEF.
Let's say an
Afrique du Nord Française, where at least in a first time, these distinct elites may be able to pull an equivalent to
Mali Federation (very rough equivalent, of course, giving the cultural and much possibly colonial differences in spite of the PoD).
How it could last in one piece, in spite of very real cultural, linguistical, political, economical, tribal, etc. differences, is anyone's guess.
But it could give enough credence for a PanMaghrebi political project, at least as a non-token political force. Not as an unified Maghreb, as in a sole country and culture. But maybe as some federative attempt, and even if it fails, as more ground for international institutions.