STATS:
Blastoise's BST is 530 and its stats are 079 in HP, 083 in Attack, 100 in Defense, 085 in Special Attack, 105 in Special Defense, and 078 in Speed.
Lapras' BST is 535 and its stats are 130 in HP, 085 in both Attack and Special Attack, 080 in Defense, 095 in Special Defense, and 060 in Speed.
MOVES:
Blastoise can learn Normal-, Water-, Dark-, and Steel-type moves through level-up. It can learn Normal-, Water-, Ice-, Fighting-, Ground-, Rock-, Dragon-, Dark-, and Steel-type moves as TMs. It can also learn Normal-, Water-, Fighting-, Psychic-, and Dragon-type moves as egg-moves.
Lapras can learn Normal-, Water-, and Ice-type moves through level-up. It can learn Normal-, Water-, Electric-, Ice-, Ground-, Psychic-, and Steel-type moves as TMs. It can also learn Normal-, Water-, Ice-, Ground-, Psychic-, Rock-, and Dragon-type moves as egg-moves.
TYPING:
Blastoise is a pure-Water-type: which makes it resistant to Fire, Water, Ice, and Steel; and weak to Electric and Grass.
Lapras is a Water/Ice-type: which makes it resistant to Water(1/2)[if it has Water Absorb as its ability, this type becomes it immunity] and Ice(1/4); and weak to Electric, Grass, Fighting, and Rock.
By stats, Lapras has a higher BST, HP stat, and Attack stat than Blastoise. They both have the same Special Attack stat of 085. Blastoise has a higher Defense stat, Special Defense stat, and Speed stat than Lapras.
By moves, Blastoise can learn 4 different types of moves through level-up compared to Lapras' three. Blastoise can learn 9 different types of moves as TMs compared to Lapras' seven. Lapras can learn 7 different types of moves as egg-moves compared to Blastoise's five.
By typing, Blastoise has two fewer weakness compared to Lapras' four. Blastoise has 4 resistances compared to Lapras' two(one if it has Water Absorb).