If the spell effect says to make an attack roll, Seeking Spell works.
When a spell description instructs you to make an attack roll, the attack is part of the spell’s effect. The rules for spellcasting in the Player's Handbook make this clear:
Each spell description in Chapter 11 begins with a block of information, including the spell's name, level, school of magic, casting time, range, components, and duration. The rest of a spell entry describes the spell's effect.
So Seeking Spell will work on any spell where making an attack roll is explicitly part of the spell’s effect. This includes booming blade, since the attack rolls is part of the spell’s effect.
However, this will not work for magic weapon, since making attacks are not a part of the spell’s effect, the effect only modifies attacks, should you choose to make them. Indeed, magic weapon says:
You touch a nonmagical weapon. Until the spell ends, that weapon becomes a magic weapon with a +1 bonus to attack rolls and damage rolls.
Magic weapon modified the properties of a weapon you touch - this is the whole effect of the spell. So Seeking Spell cannot be used with magic weapon.
It is important to note that Seeking Spell does not require the attack made to be a "spell attack", just that the attack made is part of the spell's effect:
If you make an attack roll for a spell and miss...