You should definitely dilute the malt extract before adding to the carboy - this is to ensure that it is sanitary, that it mixes evenly in the carboy and to make it easier to handle.
Many kits in fact require boiling the extract in ca. 2-3 times the amount of water to help reduce the viscosity of the liquid. Even if the kit says no boil, it's often just a marketing ploy, and it's still a good idea to dissolve the extract in hot (176°F/80°C) water in a pan to both soften and dilute the extract, and kill any microbes (e.g. bacteria on your tin opener) that could spoil the beer.
You can then half fill the carboy with cold water, and pour in the extract through a funnel, then top up to the target volume. Pour the extract "noisily" so that it splashes about - this will provide oxygen for the yeast.